In the area of the manufacture of packaging, for example that destined for the luxury industry, a converting machine by stamping applies patterns onto a sheet element by means of pressure. The patterns, for example usually metallized texts and/or decorations, are obtained by means of a shape to be stamped or a plate. The patterns originate from portions of a film derived from one or more stamping foils.
In the stamping machine, the sheet elements are taken off a stack located upstream, gripped by a conveyor and brought one after the other into a stamping platen press carrying the plate. The plate is mounted on the top fixed beam of the press. A stamping counterpart corresponding to the plate is mounted on the bottom mobile platen of the press. In the case of hot stamping, known as “hot foil stamping”, the plate is heated. The metallized stamping foils are driven between the running plane of the sheet elements and the top beam.
In a vertically upward movement, the bottom movable platen will press the stamping foil against each sheet element between the plate and its counterpart in order to deposit portions of film there. Once the film has been deposited, the bottom platen goes down again and the stamped sheet element is then released by the gripper bar onto a stack in a delivery in order to leave space for the new sheet element following.
In the same space of time, the stamping foil is displaced so that a new surface of the film is matched to the plate. The transport of the foils requires intermittent means for unwinding and advancing generally provided by rolls against which the foils are nipped by the pressing rollers. The motorized drive of these rolls allows for the intermittent advancing of these foils.
The majority of patterns deposited on the packaging can be realized from stamping foils with a small web width, generally not exceeding 30 cm. However, it is sometimes necessary to use stamping foils with a larger web width, typically in the order of between 50 cm and 70 cm. A set of narrower foils disposed side by side where the overall accumulated web width reaches this order of size can also be used.
The reels of stamping foils are stocked in an unwinding module. In this module, the foils are driven in order to be unwound there. The module serves for supporting the reels and for supplying the machine with the foil or foils. In numerous stamping machines, the module is like a cabinet located at the rear outside said machines. The module has a bearing structure in which are arranged one or more reel carriers, each one of which supports at least one reel. There are two systems for unwinding the stamping foil.
EP 1588968 describes one of the two systems, having a drive device for reels which are mounted so as to be freely rotatable on their respective reel carrier. The device comprises a belt which manages the advancing and braking function of the unwinding of the reel and therefore the supply of stamping foil to the machine. Rotational synchronization is ensured thanks to the friction of the belt both against a drive axle and against the reel. The belt of the device is tensioned by a spring.
However, when the operator puts the device into the active position on a reel, the belt automatically makes the reel turn. This phenomenon leads to waste of stamping foil.
A second disadvantage observed is the difficulty of putting several devices into the active position on one wide reel. Once a first device is placed into position on a larger width reel, this latter is blocked by the drive axle as the reel and the drive axle are coupled by the tensioned belt. When the operator has to put a second device into position on the same reel, the belt of the second device tries to turn this reel which is already blocked by the first device. The operator thus has to press very strongly and with a great deal of effort to put the second device on the reel. The forcing makes it difficult to place this second device in position and the foil is very greatly crumpled on the surface of the reel.
Yet another disadvantage is a shortcoming in the operating area. As the reel is unwound, it has less inertia but turns more quickly. Without disregarding the inertia of the hub, the power required is greater than for the full reel, in the case of a reel with a larger width. On account of the spring principle, the tension of the belt decreases and results in this belt sliding over its surface, at the end of the reel. In this case, it is necessary to reduce the rate in order to compensate for this phenomenon.